1. Field of the Invention
The present invention relates to a thin film containing nanocrystal particles and a method for preparing the thin film. More specifically, the present invention relates to a thin film prepared using a mixture of nanocrystal particles and a molecular precursor, in which the nanocrystal is used as a nucleus for crystal growth to minimize the grain boundaries in the thin film, and the molecular precursor is used to form the same crystal structure as the nanocrystal particles, thereby improving the crystallinity of the thin film; and a method for preparing the thin film.
2. Description of the Related Art
Flat panel displays, such as liquid crystal displays and organic electroluminescence displays, include a number of thin film transistors (“TFTs”) for driving the devices. Thin film transistors comprise a gate electrode, source and drain electrodes, and a semiconductor layer activated in response to the driving of the gate electrode. A p-type or n-type semiconductor layer functions as a semiconducting channel material in which a current flowing between source and drain electrodes is modulated by applied gate voltages.
Semiconductor materials frequently used in thin film transistors include amorphous silicon (“a-Si”) and polycrystalline silicon (“poly-Si”). In recent years, however, a great deal of research has been conducted on organic semiconductor materials, such as pentacene and polythiophene, for use as alternatives to the silicon based materials. The most essential requirement for the use of organic semiconductor materials in the fabrication of thin film transistors is that the charge carrier mobility of the organic semiconductor materials be sufficiently high so that good performance of the devices can be attained. Various attempts have been made to develop inorganic semiconductor materials, such as silicon-based semiconductor materials with covalent bonding, which can achieve high charge carrier mobility and can be prepared by low-cost processes, such as wet processes, and methods for preparing the semiconductor materials.
For example, thin film transistors have been proposed that comprise cadmium sulfide (CdS) film deposited by chemical bath deposition (“CBD”) as a semiconductor active layer (DuPont, Thin Solid Films 2003, vol. 444, 227-234.). However, this deposition method suffers from problems of low deposition speed and disadvantageous applicability to processing arising from the use of a chemical bath.
Further, CdS thin films formed by electrostatic spray-assisted vapor deposition (“ESAVD”) have been suggested as window layers of heterojunction thin film solar cells (Thin Solid Films 2000, vol. 359, p. 160-164.). According to the ESAVD technique, charged aerosol is induced toward substrates by an applied electrostatic field without the use of any high-vacuum apparatus, and hence the coating efficiency is advantageously improved. However, the ESAVD technique poses a problem in that the surface state of the thin films prepared thereby is non-uniform when compared to that of thin films prepared by spin coating.
U.S. Pat. No. 6,815,064 discloses a method for synthesizing nanocrystals composed of an inorganic metal compound, a solvent capable of coordinating to the inorganic metal compound, and a chalcogenide element. Since the size of nanocrystals that can be grown by the synthetic method disclosed therein is limited, however, the method is not suitable for practical application to semiconductor device fabrication lines.